demonstrator

Short definition from Wiktionary

Noun

1. 1
   One who demonstrates anything, or proves beyond doubt.
2. 2
   The forefinger.
3. 3
   One who takes part in a demonstration; a protester.
4. 4
   One who demonstrates products in a retail environment; a merchandiser.
5. 5
   An item, particularly a vehicle, used in demonstrations to a customer or user.
6. 6
   An assistant to a lecturer.
7. 7
   One who teaches anatomy from the dissected parts.